1. Field of the Invention
The present invention relates to a suction pipe pressure detection apparatus for detecting suction pipe pressure in an internal combustion engine. More particularly, the present invention relates to a suction pipe pressure detection apparatus for detecting suction pipe pressure in an internal combustion engine which is provided with a throttle valve for each cylinder, i.e., in a so-called independent suction type internal combustion engine.
2. Description of the Prior Art
While internal combustion engines have so far been put in operation with an optimum amount of fuel supplied and under the condition of a desired air-fuel ratio, and the combustion timing therefor has been controlled to be at optimum timing for ignition, the air intake amount for multi-cylinder engines has normally been calculated based upon the suction pipe pressure measured by a pressure sensor as an average value for all of the cylinders or detected by an airflow meter.
Recently, however, in order to enhance the operating performance of the internal combustion engine and to improve response characteristics of the engine such as acceleration response, the art of the internal combustion engine has included a throttle valve for each cylinder thereof, to construct, a so-called independent cylinder type internal combustion engine. Control techniques for such an internal combustion engine are being studied and developed.
Since the independent suction type internal combustion engine has been provided with a throttle valve for each cylinder, not only have good responses been brought about but also effective operation of the internal combustion engine has been made possible because of elimination of pressure interference among cylinders. On the other hand, however, there has been the need for providing an airflow meter, pressure sensor, or the like for each cylinder for detection of the intake air amount therefor and this has made the engine structure rather complex.
As the apparatus for detecting the intake air amount for controlling independent cylinder type internal combustion engines, the most commonly used type has been a simple structure using an airflow meter. That is, an airflow meter is fitted on the upstream side of the throttle valves where a number of suction pipes meet. For detecting the suction pipe pressure there has been proposed a system having a newly provided communicating vessel connected with each suction pipe which allows an averaged pressure to be detected.
The above described techniques, however, have some disadvantages as follows and are not yet satisfactory.
While the greatest merit of the independent cylinder type internal combustion engine is the excellence of response, the provision of the airflow meter in the portion where the suction pipes meet means that the airflow meter produces resistance to the intake air and consequently impairs the above merit.
Therefore, detection of the suction pipe pressure with accuracy becomes the most desirable technique in exercising control of the independent cylinder type internal combustion engine. But the prior art for detecting the intake air pressure through the provision of the communicating vessel connected with all the cylinders produces a new problem of pressure interference among the cylinders through the communicating vessel, and, further, it makes the structure rather complex and also costly.